1. Field of the Invention
Embodiments of the invention relate to a testing facility for simulating downhole conditions. More particularly, embodiments relate to a test bench for expanding tubular members having one or more threaded connections. Embodiments of the invention further relate to a test bench for simulating the expansion of a tubular connection downhole and for producing expanded tubular connection test samples.
2. Description of the Related Art
Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with pipe or casing to form a wellbore. After a section of the wellbore is formed by drilling, a section of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus and methods known in the art, the casing is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
Recent developments in the oil and gas exploration and extraction industries have included tubulars that are expandable downhole through the use of a cone or a swedge. Some expansion apparatus include expander tools with radially extendable members which, through fluid pressure from a run-in string, are urged outward radially from the body of the expander tool and into contact with a tubular wall. By rotating the expander tool in the wellbore and/or moving the expander tool axially in the wellbore with the extendable members actuated, a tubular can be expanded along a predetermined length.
The most challenging aspect of expanding strings of tubulars in a wellbore relates to the threaded connection between each joint of pipe. The threaded sections of the pin member and the box member are tapered and are typically formed directly into the ends of the tubular. The pin member includes helical threads extending along its length and terminates in a relatively thin “pin nose” portion. The box member includes helical threads that are shaped and sized to mate with the helical threads of the pin member during the make-up of the threaded connection. The threaded section of the pin member and the box member form a connection of a predetermined integrity intended to provide not only a mechanical connection but rigidity and fluid sealing. For example, at each end of the connection, a non-threaded portion of each piece often forms a metal-to-metal seal.
Threaded connections between expandable tubulars are difficult to successfully expand because of the axial bending (forces brought about as a tubular or connection wall is bent outwards) that takes place as an expansion member moves through the connection. For example, when a pin portion of a connector with outwardly facing threads is connected to a corresponding box portion of the connection having inwardly facing threads, the threads experience opposing forces during expansion. Typically, the outwardly facing threads will be in compression while the inwardly facing threads will be in tension. Thereafter, as the largest diameter portion of a conical expander tool moves through the connection, the forces are reversed, with the outwardly facing threads placed into tension and the inwardly facing threads in compression. The result is often a threaded connection that is loosened due to different forces acting upon the parts during expansion. Another problem relates to “spring back” that can cause a return movement of the relatively thin pin nose. Typically, threaded connections on expandable strings are placed in a wellbore in a “pin up” orientation and then expanded from the bottom upwards towards the surface. In this manner, the pin nose is the last part of the connection to be expanded. While threaded connections might have a single set of threads between the two tubulars, many expandable connections include a “two-step” thread body with threads of different diameters and little or no taper. These types of connections suffer from the same problems as those with single threads when expanded by a conical shaped expander tool.
There are a number of ways to test expandable connections but most take place above ground with the connections held in a fixture and expansion tools forced through them. The problem with this type of test is that the stress load conditions present in a wellbore are not recreated. An expandable tubular string and the connections that make up the string experience different tension and compression loads along the length of the string when expanded in a vertical wellbore. The loading in the string varies because the weight of the string above and below the connections is different along the string length. For example, the connections at the top of the tubular string are loaded with a lesser amount of compression (weight thereabove) than the connections at the bottom of the tubular string, which are loaded with a greater amount of string weight from above. Because the expander typically supports the weight of the entire string, as the expander passes through a connection, the loading changes from compression to tension. The connections at the top of the tubular string are then loaded with a greater amount of tension than the connections at the bottom of the tubular string, which are loaded with a lesser amount of string weight hanging below. If the expander is being propelled with fluid pressure, the tension load is further increased due to an end thrust at the bottom of the tubular string from the applied pressure.
In one example, the expandable tubular string may be free hanging in a vertical wellbore via a work string. The tubular string may be supported near its lower end by an expander that is connected to the work string. In the unexpanded position, the portion of the tubular string above the expander is placed in compression under the weight of the string above the expander, and the portion of the tubular string below the expander is placed in tension from the weight of the string below the expander. Fluid communication through the lower end of the tubular string may be closed, and fluid pressure may be supplied through the work string to the lower end of the tubular string. The fluid pressure may pump the expander through the tubular string, as well as aid in expansion of the string. The thrust force of the fluid pressure necessary to move the expander through the tubular string will also place the portion of the tubular string below the expander in tension. Therefore, as the expander moves from the lower end of the tubular string to the upper end, the connections along the length of the string will experience a change in load from compression to tension. In addition, the overall length of the tubular string may shrink as it is expanded. The shortening of the tubular string at one end while the opposite end is fixed, a “fixed-free” configuration, may further vary the loads. In certain situations, however, the tubular string may be prevented from shortening in length, such that the string is fixed at its ends during expansion. This “fixed-fixed” configuration may even further vary the loads provided on the tubular string by an additional tension load. In some configurations, the tubular string may be set on the bottom of the wellbore and/or anchored to the wellbore at one or more locations, which further vary the loads experienced by the tubular string during expansion.
Therefore, there exists a need for a method and apparatus for simulating the downhole expansion a threaded tubular connection in a controlled laboratory environment. There also exists a need for a method and apparatus for testing the expansion of threaded tubular connection designs under various wellbore conditions. There further exists a need for a method and apparatus for producing threaded tubular connection test samples that accurately represent expansion under wellbore conditions.